Photosensitive semiconductor based optical imagers are commonplace. In a semiconductor based imager, an array of pixels each comprise of a photosensitive junction or photodetector. When a photon with sufficient energy is incident upon and absorbed in the structure an electron-hole pair is created. To read resultant current from absorbed photons an amplifier is required. In CMOS devices an active pixel sensor (APS) has an integrated circuit for each pixel in the sensor with the photosensitive junction and amplifier built within the same material. In ultraviolet and infrared devices a readout integrated circuit (ROIC) is commonly used, where the photodetector and ROIC are made on different materials, then bonded.
In order to achieve dual mode functionality within a pixel, such as classic frame rate imaging and high frequency events, advanced APS or ROIC designs must be implemented. One such design is described in U.S. Pat. No. 6,864,965 wherein a switching control allows either high resolution readout at low frame rate or readout of reduced resolution at high frame rates.
Another such apparatus is described in U.S. Publication [US 20120261553 A1] wherein an ROIC is provided which allows for switching between different detection modes. One of the disclosed modes allows for detection of a thermal image and detection of a short laser pulse in a commonly shared readout path. This mode enables capture of a passive image and location of laser events as every frame is readout. This application relates to another approach.